1. Field of the Invention
The present invention relates to data processing apparatuses, data processing methods, and portable communication terminal apparatuses. Particularly, the present invention relates to a data processing apparatus, a data processing method, and a portable communication terminal apparatus which are capable of performing high-speed data processing in, for example, an integrated circuit (IC) (large scale integration (LSI)) for contactless communication.
2. Description of the Related Art
Non-contact type IC card systems, which are well known as contactless communication systems, are often used in, for example, automatic ticket gates in stations.
FIG. 1 is a diagram schematically showing the structure of an IC card system in related art.
The IC card system in the related art includes a reader-writer (R/W) 1 and an IC card 2.
The R/W 1 transmits a radio signal to generate a radio-frequency (RF) field (electromagnetic field).
The IC card 2 has an antenna 11 composed of a loop coil and an LSI 12 for contactless communication.
When the IC card 2 comes close to the R/W 1 and enters the RF field that has a strength greater than a predetermined strength and that is generated by the R/W 1, the IC card 2 receives power produced by electromagnetic induction caused by the radio signal transmitted from the R/W 1 to start to operate. The IC card 2 performs data processing, for example, transmits and receives data to and from the R/W 1 by radio signals.
In other words, since the IC card 2 does not include a power supply, the IC card 2 receives the power produced by the electromagnetic induction in the antenna 11 (loop coil), caused by the radio signal transmitted from the R/W 1, to operate the LSI 12 and performs a variety of data processing.
The LSI 12 in the IC card 2 receives the power produced by the electromagnetic induction caused by the radio signal transmitted from the R/W 1 to operate in the manner described above. The power caused by the radio signal transmitted from the R/W 1 is reduced in the IC card 2 as the distance between the R/W 1 and the IC card 2 becomes longer.
For example, if the IC card 2 receives power E1 that is not less than power E0 and that is caused by the radio signal transmitted from the R/W 1 where E0 denotes the minimum power for the LSI 12 in the IC card 2 to operate, when the IC card 2 is located at a position P1 relatively near to the R/W 1, the LSI 12 can operate at the position P1 to perform a variety of data processing.
In contrast, if the IC card 2 only receives power E2 that is less than the power E0 and that is caused by the radio signal transmitted from the R/W 1 when the IC card 2 is located at a position P2 farther away from the R/W 1 than the position P1, the LSI 12 cannot operate at the position P2.
Accordingly, the LSI 12 in the IC card 2 can operate only within a range near to the R/W 1.
Increasing the level of the radio signal output from the R/W 1 can expand the range in which the IC card 2 can operate. However, the output from the R/W 1 is restricted by the radio law or interference with a radio signal output from another R/W can cause a problem.
Hence, it is necessary to limit the level of the radio signal in the R/W 1, and the IC card 2 is designed in consideration of low power consumption such that the IC card 2 can operate with the power caused by the radio signal having the limited level.
The LSI 12 operates in synchronization with a clock. Setting the frequency of the clock to a lower value (setting the period of the clock to a longer value) is effective in saving the power consumption in the LSI 12, and the IC card 2 is designed such that the LSI 12 operates in synchronization with the clock having a sufficiently low frequency.
Since it takes some time to perform the data processing in the LSI 12, it is necessary for a user to stay at a position, where the LSI 12 can receive the power sufficient for the LSI 12 to operate from the R/W 1, for at least a time required for the data processing in the LSI 12 and to hold the IC card 2 over the R/W 1.
Incorporating the function of the IC card 2 into a portable apparatus, such as a portable telephone, has been proposed in recent years. Since the portable telephone has, for example, a battery pack serving as an internal power supply that causes the portable telephone to operate, the LSI 12 can operate even when the IC card 2 is away from the R/W 1 by allowing the IC card 2 incorporated in the portable telephone to receive the power from the internal power supply.
An apparatus and a method of seamlessly switching between the power supply that receives the power caused by the radio signal transmitted from the R/W 1 and the internal power supply in the portable telephone to supply the power to the LSI 12, when the function of the IC card is incorporated in the portable telephone, are proposed in, for example, Japanese Unexamined Patent Application Publication No. 2003-036427 (Patent Document 1).